Red Tests were fixed

Unused 'using' directive were removed.

Octokit.Tests/Exceptions/TwoFactorRequiredExceptionTests.cs

@@ -1,9 +1,5 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
+using System.Collections.Generic;
 using System.Net;
-using System.Text;
-using System.Threading.Tasks;
 using Octokit.Internal;
 using Xunit;
 
@@ -11,7 +7,7 @@ namespace Octokit.Tests.Exceptions
 {
     public class TwoFactorRequiredExceptionTests
     {
-        public class TheConstructor
+        public class TheCtor
         {
             [Fact]
             public void SetsDefaultMessage()